The present disclosure relates generally to nacelle bodies suitable for use with wind turbines. In particular, shrouded wind turbines using such nacelle configurations are described herein.
Conventional horizontal axis wind turbines (HAWTs) have 2-5 blades and are oriented or pointed into the wind by computer controlled motors. These turbines typically require a supporting tower ranging from 60 to 90 meters (200-300 feet) in height. The blades generally rotate at a rotational speed of about 10 to 22 rpm, with tip speeds reaching over 200 mph. A gear box is commonly used to step up the speed to drive the generator, although some designs may directly drive an annular electric generator. Some turbines operate at a constant speed. However, more energy can be collected by using a variable speed turbine and a solid state power converter to interface the turbine with the generator. Although HAWTs have achieved widespread usage, their efficiency is not optimized. In particular, they will not exceed 59.3% efficiency, i.e., the Betz limit, in capturing the potential energy of the wind passing through it.
Several problems are associated with HAWTs in both construction and operation. The tall towers and long blades are difficult to transport. Massive tower construction is required to support the heavy blades, gearbox, and generator. Very tall and expensive cranes and skilled operators are needed for installation. In operation, HAWTs require an additional yaw control mechanism to turn the blades toward the wind. HAWTs typically have a high angle of attack on their airfoils that do not lend themselves to variable changes in wind flow. HAWTs are difficult to operate in near ground, turbulent winds. Furthermore, ice build-up on the nacelle and the blades can cause power reduction and safety issues. Tall HAWTs may affect airport radar. Their height also makes them obtrusively visible across large areas, disrupting the appearance of the landscape, which may be objectionable. Finally, downwind variants suffer from fatigue and structural failure caused by turbulence.
The various components of the HAWT, such as the gearbox, the rotor shaft, generator, pitch and yaw controls, and brakes, are generally located within the nacelle of the HAWT. The nacelle may have dimensions such as 24 meters in length by 6 meters in height by 6 meters in width (˜79 ft long×20 ft high×20 ft wide). The nacelle usually weighs at least 10 tons, and can weigh as much as 60 tons. The nacelle itself is usually made from two pieces, a bottom and a top. The bottom piece of the nacelle is anchored to the tower, the various components are placed inside the bottom piece, and the nacelle is completed by placing the top piece to cover all of the various components. The resulting outer surface of the nacelle is generally not smooth, flat, or even. The nacelle may not enhance the efficiency of energy generation in the wind turbine.